MirOS Manual: disk(9), disk_attach(9), disk_busy(9), disk_detatch(9), disk_find(9), disk_init(9), disk_resetstat(9), disk_unbusy(9)

DISK(9)                       BSD Kernel Manual                        DISK(9)


     disk - generic disk framework


     #include <sys/types.h>
     #include <sys/disklabel.h>
     #include <sys/disk.h>


     disk_attach(struct disk *);

     disk_detach(struct disk *);

     disk_busy(struct disk *);

     disk_unbusy(struct disk *, long bcount, int read);

     disk_resetstat(struct disk *);

     struct disk *
     disk_find(char *);


     The OpenBSD generic disk framework is designed to provide flexible, scal-
     able, and consistent handling of disk state and metrics information. The
     fundamental component of this framework is the disk structure, which is
     defined as follows:

     struct disk {
             TAILQ_ENTRY(disk) dk_link;      /* link in global disklist */
             char     *dk_name;      /* disk name */
             int      dk_bopenmask;  /* block devices open */
             int      dk_copenmask;  /* character devices open */
             int      dk_openmask;   /* composite (bopen|copen) */
             int      dk_state;      /* label state */
             int      dk_blkshift;   /* shift to convert DEV_BSIZE to blks */
             int      dk_byteshift;  /* shift to convert bytes to blks */

              * Metrics data; note that some metrics may have no meaning
              * on certain types of disks.
             int       dk_busy;      /* busy counter */
             u_int64_t dk_xfer;      /* total number of transfers */
             u_int64_t dk_seek;      /* total independent seek operations */
             u_int64_t dk_bytes;     /* total bytes transferred */
             struct timeval  dk_attachtime;  /* time disk was attached */
             struct timeval  dk_timestamp;   /* timestamp of last unbusy */
             struct timeval  dk_time;        /* total time spent busy */

             struct  dkdriver *dk_driver;    /* pointer to driver */

              * Disk label information.  Storage for the in-core disk label
              * must be dynamically allocated, otherwise the size of this
              * structure becomes machine-dependent.
             daddr_t  dk_labelsector;        /* sector containing label */
             struct disklabel *dk_label;     /* label */
             struct cpu_disklabel *dk_cpulabel;

     The system maintains a global linked-list of all disks attached to the
     system. This list, called disklist, may grow or shrink over time as disks
     are dynamically added and removed from the system. Drivers which current-
     ly make use of the detachment capability of the framework are the ccd(4)
     and vnd(4) pseudo-device drivers.

     The following is a brief description of each function in the framework:

     disk_init()       Initialize the disklist and other data structures used
                       by the framework. Called by main() before autoconfi-

     disk_attach()     Attach a disk; allocate storage for the disklabel, set
                       the "attached time" timestamp, insert the disk into the
                       disklist, and increment the system disk count.

     disk_detach()     Detach a disk; free storage for the disklabel, remove
                       the disk from the disklist, and decrement the system
                       disk count. If the count drops below zero, panic.

     disk_busy()       Increment the disk's "busy counter". If this counter
                       goes from 0 to 1, set the timestamp corresponding to
                       this transfer.

     disk_unbusy()     Decrement a disk's busy counter. If the count drops
                       below zero, print a warning message. Get the current
                       time, subtract it from the disk's timestamp, and add
                       the difference to the disk's running total. Set the
                       disk's timestamp to the current time. If the provided
                       byte count is greater than 0, add it to the disk's run-
                       ning total and increment the number of transfers per-
                       formed by the disk. The third argument read specifies
                       the direction of I/O; if non-zero it means reading from
                       the disk, otherwise it means writing to the disk.

     disk_resetstat()  Reset the running byte, transfer, and time totals.

     disk_find()       Return a pointer to the disk structure corresponding to
                       the name provided, or NULL if the disk does not exist.

     The functions typically called by device drivers are disk_attach(),
     disk_detach(), disk_busy(), disk_unbusy(), and disk_resetstat(). The
     function disk_find() is provided as a utility function.


     This section includes a description on basic use of the framework and ex-
     ample usage of its functions. Actual implementation of a device driver
     which utilizes the framework may vary.

     A special routine, disk_init(), is provided to perform basic initializa-
     tion of data structures used by the framework. It is called exactly once
     by the system, in main(), before device autoconfiguration.

     Each device in the system uses a "softc" structure which contains auto-
     configuration and state information for that device. In the case of
     disks, the softc should also contain one instance of the disk structure,

     struct foo_softc {
             struct  device *sc_dev;         /* generic device information */
             struct  disk *sc_dk;            /* generic disk information */
             [ . . . more . . . ]

     In order for the system to gather metrics data about a disk, the disk
     must be registered with the system. The disk_attach() routine performs
     all of the functions currently required to register a disk with the sys-
     tem including allocation of disklabel storage space, recording of the
     time since boot that the disk was attached, and insertion into the disk-
     list. Note that since this function allocates storage space for the disk-
     label, it must be called before the disklabel is read from the media or
     used in any other way. Before disk_attach() is called, a portion of the
     disk structure must be initialized with data specific to that disk. For
     example, in the "foo" disk driver, the following would be performed in
     the autoconfiguration "attach" routine:

     fooattach(parent, self, aux)
             struct device *parent, *self;
             void *aux;
             struct foo_softc *sc = (struct foo_softc *)self;
             [ . . . ]

             /* Initialize and attach the disk structure. */
             sc->sc_dk.dk_driver = &foodkdriver;
             sc->sc_dk.dk_name = sc->sc_dev.dv_xname;

             /* Read geometry and fill in pertinent parts of disklabel. */
             [ . . . ]

     The foodkdriver above is the disk's "driver" switch. This switch current-
     ly includes a pointer to the disk's "strategy" routine. This switch needs
     to have global scope and should be initialized as follows:

     void    foostrategy(struct buf *);
     struct  dkdriver foodkdriver = { foostrategy };

     Once the disk is attached, metrics may be gathered on that disk. In order
     to gather metrics data, the driver must tell the framework when the disk
     starts and stops operations. This functionality is provided by the
     disk_busy() and disk_unbusy() routines. The disk_busy() routine should be
     called immediately before a command to the disk is sent, e.g.:

             struct foo_softc *sc;
             [ . . . ]

             /* Get buffer from drive's transfer queue. */
             [ . . . ]

             /* Build command to send to drive. */
             [ . . . ]

             /* Tell the disk framework we're going busy. */

             /* Send command to the drive. */
             [ . . . ]

     When disk_busy() is called, a timestamp is taken if the disk's busy
     counter moves from 0 to 1, indicating the disk has gone from an idle to
     non-idle state. Note that disk_busy() must be called at splbio(). At the
     end of a transaction, the disk_unbusy() routine should be called. This
     routine performs some consistency checks, such as ensuring that the calls
     to disk_busy() and disk_unbusy() are balanced. This routine also performs
     the actual metrics calculation. A timestamp is taken, and the difference
     from the timestamp taken in disk_busy() is added to the disk's total run-
     ning time. The disk's timestamp is then updated in case there is more
     than one pending transfer on the disk. A byte count is also added to the
     disk's running total, and if greater than zero, the number of transfers
     the disk has performed is incremented.

             struct foo_xfer *xfer;
             struct foo_softc = (struct foo_softc *)xfer->xf_softc;
             struct buf *bp = xfer->xf_buf;
             long nbytes;
             [ . . . ]

              * Get number of bytes transferred.  If there is no buf
              * associated with the xfer, we are being called at the
              * end of a non-I/O command.
             if (bp == NULL)
                     nbytes = 0;
                     nbytes = bp->b_bcount - bp->b_resid;

             [ . . . ]

             /* Notify the disk framework that we've completed the transfer. */
             disk_unbusy(&sc->sc_dk, nbytes);

             [ . . . ]

     Like disk_busy(), disk_unbusy() must be called at splbio().

     At some point a driver may wish to reset the metrics data gathered on a
     particular disk. For this function, the disk_resetstat() routine is pro-


     The disk framework itself is implemented within the file
     sys/kern/subr_disk.c. Data structures and function prototypes for the
     framework are located in sys/sys/disk.h.

     The OpenBSD machine-independent SCSI disk and CD-ROM drivers utilize the
     disk framework. They are located in sys/scsi/sd.c and sys/scsi/cd.c.

     The OpenBSD ccd(4), raid(4) and vnd(4) drivers utilize the detachment ca-
     pability of the framework. They are located in sys/dev/ccd.c,
     sys/dev/raidframe/, and sys/dev/vnd.c.


     ccd(4), raid(4), vnd(4), spl(9)


     The OpenBSD generic disk framework first appeared in NetBSD 1.2.


     The OpenBSD generic disk framework was architected and implemented within
     NetBSD by Jason R. Thorpe <thorpej@NetBSD.ORG>.

MirOS BSD #10-current          January 7, 1996                               3

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